Various approaches to improve the efficiency of electric cleaners for removing dust embedded in carpet have been reported and also marketed. However, none of the approaches is satisfactory and their cleaning efficiency cannot exceed a certain limitation. In particular, they are very poor for cleaning long pile carpet.
The following discussion reviews known approaches and comments on the reasons for their low efficiency.
A simple approach involves a straight air suction head. The suction head includes a rectangular suction box having a long left to right, hereafter abbreviated as "L-R", dimension and a short fore to back, hereafter abbreviated as "F-B", dimension. The lower face of the suction head has a long L-R opening for sucking dust. The lowest ends of the front and back walls of the suction head contact a carpet surface and suction flows through the pile just under the walls removing dust in the flow path.
In this simple case, air flow path in the pile is located near the lowest ends of the walls in a short-circuited manner between the outer and inner air of the wall and cannot extend to the deep or bottom region of carpet pile. This is the reason for the low efficiency. Increased fan motor power can increase flow speed/volume in the short-circuit path, but cannot extend the path to deeper regions. Dust can be dislodged and removed from the pile at a flow speed over a certain threshold velocity: Vth. Too much of an increase in flow velocity over Vth is meaningless.
A second known approach to carpet cleaning incorporates mechanical agitation such as vibration or beating. However, cleaners including mechanical agitation are not currently on the market due to their noise. Mechanical agitation is basically ineffective, because such agitation cannot reach to deep/bottom regions of carpet. Additionally, the air flow to convey the dislodged dust cannot reach to the deep/bottom regions of the carpet.
A third widely used approach incorporates a rotating brush made of rubber or bristles, driven by a motor or an air turbine. It is expected that such agitation with the brush may be effective to dislodge dust in pile.
It is, in fact, fairly effective, but cannot extend beyond certain limitations. For example, such agitation also cannot reach to the deep/bottom regions. Furthermore, a powerful high-speed rotating brush very easily removes pile fibers from carpet. This defect is fatal for a high-grade, expensive carpet.
A fourth approach includes many slender finger-like pipes (hereafter referred to as "finger pipes") vertically arranged in a cleaning head. In such a device, pressurized fan-afterflow is fed to the top of the pipes. The pipes' flow blows out from the bottom end of the pipes to clean the pile.
Similarly, L-R extending slits are vertically arranged in the head and the blowing flow is directed to the surface of the carpet. The finger-pipe example, disclosed in Japanese Laid Open Pat. SHOU 50-155057 (Negishi), is shown in FIG. 14.
Examples of finger-pipes fed with room air (atmospheric pressure) are disclosed in Japanese Laid Open Pat. SHOU 63-122415 (Ariyoshi), HEI 1-256920 (Kadowaki). An example of small holes fed with room air is disclosed in Japanese Laid Open Utility Pat. SHOU 51-95266 (Nagasima). An example of a slit fed with room air is disclosed in Japanese Laid Open Utility Pat. SHOU 54-138467 (Urusibara).
In the above examples that include air either pressurized or room air directed to carpet, the bottom ends of the finger-pipes, the small holes, and the slit do not extend downward beneath the lowest ends of the head walls and only blow on the carpet surface.
These means that merely blow air toward the carpet surface are not effective, as the blowing air cannot penetrate into the deep regions of the pile due to the high flow resistance of pile.
The inventor of the present invention also disclosed a fifth approach in U.S. Pat. No. 5,647,092, including Pile Gorge Forming by means of mechanical contact with pile top. This gorge also has the effect of directing air flow reaching the bottom of the pile. However, its expected effect is decreased due to the following two reasons. The recirculated air jet, directed to the gorge, blows out the dust in the gorge bottom into suction air flow, but, unfortunately, also into the piles constituting both side walls of the gorge. An upflowing stream in the piles functioning to take out the dust is to be formed incorporating with the incoming flow through the piles just under the front and back walls. However, the flow resistance of pile is too high to form such an upstream.
A sixth approach to improve cleaning efficiency includes finger pipes extending downward into piles beneath the lowest ends of the walls at the cleaning head. An example of the sixth approach fed with pressurized air, as shown in FIGS. 15A and 15B, is disclosed in U.S. Pat. No. 3,268,942 to Rossnan. Another example fed with room air, as shown in FIGS. 17A and 17B, is disclosed in U.S. Pat. No. 4,594,749 to Waterman. A finger pipe array used solely for sucking air in piles, as shown in FIGS. 16A and 16B, is disclosed in U.S. Pat. No. 3,611,473 to Johnson.
This sixth approach can be expected to overcome the limitation that other known approaches discussed above cannot generate air flow to reach to the deep/bottom region of the carpet, because the tip or lowest end of the finger pipe can enter deep into the carpet.
However, this sixth approach is still insufficient. The fault is due to the finger pipe shape. The air just blowing out from the tip or lowest end of the finger pipe may have sufficient speed to dislodge the dues in the pile. However, the air speed decreases rapidly below the threshold Vth, as the air flows away from the tip in a two dimensional manner near the tip and then immediately diffuses upward in a three-dimensional manner. As a result, cleanable area is very localized to a region (.delta. in diameter) near the tip. Additionally, too greatly decreased flow speed cannot convey the dislodged dust through pile.
Furthermore, during the cleaning head stroke (stroke speed: Vst), an exposed time (Tex) of specific pile fiber to a speed flow higher than Vth (Tex=.delta./Vst) is too short to dislodge any dust in the pile. Such exposed time Tex has to be longer than a certain threshold value Tth.
A seventh approach to improve cleaning efficiency is disclosed by Takemura (Japanese Laid Open Pat. SHOU 54-158066, and SHOU 55-153). Takemura discloses a head that has plural downwardly opening slits partly provided, as shown in FIGS. 18 B-1 and B-2, on a front wall lower face and fed with room air from openings provided in the foreside of the front wall, as shown in FIG. 18A.
At first glance, these slits may lead air flow into piles. However, the lower face of the front wall is flat, as shown in FIG. 18A, so the lower face cannot sink deep into piles. Takemura is only aiming to distribute suction power, P, more uniformly along an L-R direction as illustrated by curve "a" than the conventional distribution illustrated by curve "b", as shown in FIG. 18C.